PHRASAL VERB 捧腹大笑;笑得前仰后合 If you say that people are falling about, you mean that they are laughing a lot about something. 捧腹大笑;笑得前仰后合 [British, informal] [Also VPwith n]
Dan fell about and slapped his thighs. [VERBPREP.]
丹笑得前仰后合，直拍大腿。
The men at the table fell about laughing. [VERBPREP. verb-ing]